Textural and capacitive characteristics of MnO2 nanocrystals derived from a novel solid-reaction route

Nanostructured manganese dioxide (MnO2) materials were synthesized via a novel room-temperature solid-reaction route starting with Mn(OAc)2·4H2O and (NH4)2C2O4·H2O raw materials. In brief, the various MnO2 materials were obtained by air-calcination (oxidation decomposition) of the MnC2O4 precursor at different temperatures followed by acid-treatment in 2 M H2SO4 solution. The influence of calcination temperature on the structural characteristics and capacitive properties in 1 M LiOH electrolyte of the MnO2 materials were investigated by X-ray diffraction (XRD), infrared spectrum (IR), transmission electron microscope (TEM) and Brunauer–Emmett–Teller (BET) surface area analysis, cyclic voltammetry, ac impedance and galvanostatic charge/discharge electrochemical methods. Experimental results showed that calcination temperature has a significant influence on the textural and capacitive characteristics of the products. The MnO2 material obtained at the calcination temperature of 300 °C followed by acid-treatment belongs to nano-scale column-like (or needle-like) γ,α-type MnO2 mischcrystals. While, the MnO2 materials obtained at the calcination temperatures of 400, 500, and 600 °C followed by acid-treatment, respectively, belong to γ-type MnO2 with the morphology of aggregates of crystallites. The γ,α-MnO2 derived from calcination temperature of 300 °C exhibited a initial specific capacitance lower than that of the γ-MnO2 derived from the elevated temperatures, but presented a better high-rate charge/discharge cyclability.